The main objectives of this proposal are: 1) The study of the DNA rearrangements which are promoted by polyoma virus elements in transformed cells, and the comparison of these rearrangements with similar phenomena controlled by cellular events. 2) The study of the regulation of transcription of integrated polyoma virus genomes by cis DNA elements and transactivatinf or transrepressing proteins. 3) The cloning and characterization of genes controlling cell cycle progression in animal cells, as defined by ts mutants of the BHK hamster cell line specifically blocked in cell cycle progression. 4) The study of the control of transcription of specific cellular genes in the cycle of normal or virus transformed cells. 5) The study of the nature of Kaposi's Sarcoma in AIDS patients. Our main long range objective is to understanding of what patterns of regulation are altered in transformed cells. To this aim the studies of polyoma promoted gene rearrangements and of the expression of integrated polyoma genomes should shed light on the factors controlling, the expression of transforming genes, as well as on the effect that transforming gene-products have on the transcription of other cellular genes. The study of cell cycle genes and of the regulation of gene expression during the cell cycle should provide information on what differentiates the control of cell division of cancer cells from that of normal cells.